Beginner Dumble build?

[beasleybodyshop]

Of all the Dumble amp designs (minus the D-lator) Which one would be a good first build? I know all the Dumble designs are not exactly a Fender Princeton in terms of simplicity, which one would be a good start?

[ToneMerc]

For a first Dumble build, it doesn't get much simplier than this.

https://tubeamparchive.com/viewtopic.php?t=18363



https://tubeamparchive.com/download/file.php?id=28838

TM

[beasleybodyshop]

That is just too cool. Definitely adding this one to my build list. Thanks Merc!

[beasleybodyshop]

So what is up with the pot under the chassis on the layout? The one with the 27K resistor. What is that controlling? And better yet, what would the spec be on those 6 diodes? And what are those diodes doing for the circuit? Sorry for all the questions lol

[dcribbs1412]

So what is up with the pot under the chassis on the layout? The one with the 27K resistor. What is that controlling? And better yet, what would the spec be on those 6 diodes? And what are those diodes doing for the circuit? Sorry for all the questions lol

Pot is for bias(idle power tubes)
diodes are for rectifier...most likely 1n4007 diodes
some simple somewhat accurate explanations I found on Google.
Hope this helps...good luck

Darin

This is a question I’ve heard a lot. What does a rectifier do? If you don’t know, don’t feel bad, you’re about to find out. A rectifier changes alternating current (AC), like a wall outlet, to direct current (DC) that is required to run all electronics inside your amplifier. That’s it, it’s really that simple. The AC voltage comes from the wall into the transformer of your amp where it is then run through the rectifier to get DC voltage. This is before all audio circuitry so an important thing to realize is that NO AUDIO SIGNAL PASSES THROUGH THE RECTIFIER. It is purely for voltage conversion.

The best way to understand bias is to think of it like the idle setting on a car. Nowadays most cars have complex computers that control the idle, however, in the end the process is still basically the same as it has always been. The fuel and air mixture is adjusted so that the motor runs smoothly; too much of either and the motor won't run very well or even possibly not at all. The idea is to find the perfect balance for optimum performance. When it comes to tube amps the idea is basically the same, however, instead of fuel and air we are dealing with electrical current. The purpose of setting the bias of an amp is to find the optimum setting for the flow of current when the amp is idling. Too much and the life of a tube is significantly decreased and in extreme cases failure can occur; this is also referred to as "biased hot." Too little and unpleasant distortion (crossover distortion) is produced; this is referred to as "biased cold." The correct setting is crucial for an amp to perform at its best both functionally and soundwise.

[beasleybodyshop]

Oh yeah! I should have figured that out duh lol. I notice most amps have 2 or 4 for rectification but that one has 6? What would be the reason for that? Also the indicator light has no wires to it? What does the mini toggle switch do? And am I correct in assuming the input jacks are grounded through the chassis with a lock washer? Thanks.

[martin manning]

Three diodes on each leg just makes triple-redundancy. That layout is a bit incomplete, and I'd assume untested. The pilot should be connected to the filament supply, and there should be a ground wire from the input jacks to the chassis, although that isn't strictly necessary. The mini-toggle appears to be a bright switch, but the yellow wire from V1 pin 7 should go to the center lug on the switch with the other yellow wire, and the thing that looks like a resistor should be a small capacitor around 100-500pF.

[ToneMerc]

Oh yeah! I should have figured that out duh lol. I notice most amps have 2 or 4 for rectification but that one has 6? What would be the reason for that? Also the indicator light has no wires to it? What does the mini toggle switch do? And am I correct in assuming the input jacks are grounded through the chassis with a lock washer? Thanks.

6 ( 3 in series) diodes are configured as Fender did it, simply a holdover from when silicon diodes were only available in 200-300v ratings.

a simple omission, everything you need to build the amp is there, research and study Fender layouts, use the forum search function here as well.

bright switch

yes

TM

[M Fowler]

https://tubeamparchive.com/download/file.php?id=28952

[beasleybodyshop]

https://tubeamparchive.com/download/file.php?id=28918

Thanks M. Fowler, that does seem to answer most of the other questions I was going to ask lol.

Also, aren't there supposed to be heater wires on pins 2 and 7 on the output tubes?

[M Fowler]

Yes heater wires but to keep the layout clean we don't put the heater wires in.

[beasleybodyshop]

Oh, nevermind, I see that they are indicated, just no wires drawn to them. Are the heater wires not drawn from the PT either?

[M Fowler]

Correct left out filament wires to pilot light as well as tube sockets.

Also, I would use a different can cap perhaps 20/20/20/20 connecting two 20uf's together for total 40uf on the B+1 that leaves you two 20uf connections for the board.

Or a 80uf/20uf/20uf can cap.

[beasleybodyshop]

Correct left out filament wires to pilot light as well as tube sockets.

Also, I would use a different can cap perhaps 20/20/20/20 connecting two 20uf's together for total 40uf on the B+1 that leaves you two 20uf connections for the board.

Or a 80uf/20uf/20uf can cap.

Ok. Whats your reasoning behind changing the can cap?

[M Fowler]

So you don't have figure out how to glue or tie down the floating 20uf cap on the right end of the tone board. A stock Princeton would already have 20/20/20/20 can cap and if a guy was using after market Princeton chassis or a bare chassis you would be ordering parts so why not get the correct can cap or put the axial caps on the tone board. Many ways to build this amp.

Maybe this version of the layout is better.

EDIT: Version 3 layout updated.